Conventional mechanical testing machines used for such tests normally require difficult settings in order to obtain a strictly uniaxial stress, i.e. a pure and uniform compression on the specimen. They are generally constituted by two facing parts (by planar faces) and wherein one is a fixed support and the other a mobile piston. The sample is compressed by the advance of the piston, but long and difficult operations are necessary in order to reestablish a correct alignment of the two parts.